Conversion of analog images into digital data has become widespread for a variety of applications, including storing, manipulating, transmitting and displaying or printing copies of the images. For example, images captured in photographic media are being converted to digital data and stored on compact discs for readout and display as a video image or for printing with various types of color printers. In order to capture the photographic image digitally, the image frame is scanned with a light beam or line, and the light transmitted through the image is detected, typically as three primary color light intensity signals, and digitized. The digitized values may be formatted to a standard for video display and stored on compact disc or magnetic media. Such film digitizers take a variety of forms and the various common aspects of film digitizing, particularly line illumination and linear CCD-based digitizers, are described in greater detail in commonly assigned U.S. Pat. No. 5,012,346.
In the field of color scanners, such as described above, as well as elsewhere in the fields of capturing real images and copying recorded images using light, as well as in other areas, there is often a need to provide a filter in a given light path. Such filters, like most components of an optical system, are typically held firmly in the required position. This is true in particular in color scanners. In some color scanners it is necessary to provide a filter in the optical path, that is between an image to be scanned and a sensor. For example, the scanner may have a lens between the image location for scanning and the sensor, and a filter between the lens and the sensor. A useful class of filters for this and other purposes, are those known as WRATTEN filters available from Eastman Kodak Company, Rochester, N.Y. Such filters are made of a dye containing gelatin layer on a polyester base. The dye or dyes in the gelatin are chosen for the desired absorption profile.
Filters of the above type can, however, contract and expand in all three dimensions with changes in humidity and temperature. This contraction/expansion range is quite low, for example being only in the neighborhood of about 3% in each dimension. In most applications this has no noticeable effect. However, in the field of color scanners where light from the image being scanned is concentrated in a narrow beam before falling upon the sensor, dimensional changes in optical components between the location of an image to be scanned and the sensor can be critical. Many arrangements for clamping filters and the like have been previously known. For example, various arrangements are described in U.S. Pat. No. 2,444,520; U.S. Pat. No. 2,503,714; U.S. Pat. No. 4,575,230; U.S. Pat. No. 4,823,245; U.S. Pat. No. 2,009,145; U.S. Pat. No. 2,589,680; U.S. Pat. No. 2,498,278; and U.S. Pat. No. 4,383,735. However, such arrangements rigidly clamp the filter in position without allowance for contraction/expansion.
It would be desirable then, to ensure that changes in filter dimensions due to expansion/contraction under different environmental conditions, will not have an adverse effect on an optical apparatus using such a filter. It would be particularly desirable to ensure that in a scanner, changes in dimensions of a filter positioned in the optical path between the image to be scanned and a sensor, do not cause distortion of the image received by the sensor.